1. Field of the Invention
The invention mainly relates to genes for controlling floral development in orchid. In particular, the invention relates to genes for controlling sepal, petal, lip, and stamen developments.
2. Description of the Related Art
Phalaenopsis spp., which has a single axis stem, is a member of Orchidaceae family. It is one of the most important ornamental flowers exporting from Taiwan, and has been selected for developing as a delicate agriculture industry. Phalaenopsis attracts people by its elegant floral morphology. The Phalaenopsis with special floral morphology has a high value in the market.
The flowers of general monocots or eudicots have different types of organs arranged in concentric whorls. The outermost whorl contains sepals and the next whorl contains petals. The third whorl contains the stamens. Furthermore, the female reproductive organs occupy the center of the flower. In the modern molecular biotechnology, a plant having a special floral morphology can be bred by changing the expression of genes for controlling flower development based on the understanding of the regulation mechanism of floral development. In the model plants such as Arabidopsis and snapdragon, the genes for controlling floral development and mechanism thereof are well studied (Weigel, D. and Meyerowitz, E. M. 1994. The ABCs of floral homeotic genes. Cell 78, 203–209). In the model plants, the flower controlling mechanism is “ABC model” in which three flower controlling genes A, B and C alone or in combination control the flower organ development. Expression of A alone specifies sepal formation. The combination of AB specifies the development of petals, and the combination of BC specifies the stamen formation. Expression of C alone determines the development of carpels (Theissen et al., 2000. A short history of MADS-box genes in plants. Plant Mol. Biol. 42, 115–149).
These genes A, B and C are all transcription factor genes and the gene products thereof have a MIKC-type domain structure comprising a MADS-box (M) domain, an intervening (I) domain, a keratin-like (K) domain, and a C-terminal (C) domain. The MADS-box domain is considered to play an important role in controlling floral development in Arabidopsis and snapdragon (Weigel and Meyerowitz, 1994).
All B-function genes belong to the family of MADS-box genes and fall into either one of two different clades, namely DEF— or GLO-like genes (Theissen et al., 1996, Classification and phylogeny of the MADS-box multigene family suggest defined roles of MADS-box gene subfamilies in the morphological evolution of eukaryotes. J. Mol. Evol. 43, 484–516). DEF- and GLO-like genes are closely related to the MADS-box gene family. These two clades together also represent a well supported gene lade (Theissen et al., 1996). In addition to the higher eudicots, B genes have been most intensively studied in cereal grasses (family Poaceae), mainly the important crop plants and rice and maize model system (Moon et al., 1999. Identification of a rice APETALA3 homologue by yeast two-hybrid screening. Plant Mol. Biol. 40, 167–177; Ambrose et al., 2000. Molecular and genetic analyses of the silkyl gene reveal conservation in floral organ specification between eudicots and monocots. Mol. Cell 5, 569–579; Münster et al., 2001. Characterization of three GLOBOSA-like MADS-box genes from maize: evidence for ancient paralogy in one class of floral homeotic B-function genes of grasses. Gene 262, 1–13). In the literature, only one DEF-like gene has been reported in diverse monocots such as lily (Lilium regale), wheat (Triticum aestium), maize and rice (Münster et al., 2001).
The orchid flower does not have the normal monocots and eudicots floral morphology. It has three sepals, three petals and one of the petals possesses a different morphological structure known as the lip. The male and female reproductive parts are combined in a uniform structure, the column, in the center of the flower. The pollen grains stick together to form pollinia located at the upper end of the column inside the anther (referring to FIG. 1a). As a reason, the result established in the model plant cannot be applied in constructing the mechanism of the elegant orchid floral morphology. In the prior art, the traditional breeding technique is still used in changing the orchid floral morphology. It spends a lot of time and the success rate is also low.